The present invention relates to energy joints biased with a torsion spring, such as are sometimes used for biasing the back of an office chair to an upright position. However, the present invention is not believed to be limited to office chairs, nor to furniture. Instead, it is contemplated that the present torsional energy joint is useful in many different applications, particularly high-volume assembly situations, where it is desirable to provide a torsional joint with pre-tension.
Chairs often have reclineable backs for increased comfort. The reclineable backs are typically biased toward an upright position in a manner that both supports a person""s upper torso when leaning rearwardly, yet that also permits a comfortable recline that feels secure during the reclining motion. Many different types and styles of biasing mechanisms are known in the art. However, improvements are desired to overcome various problems. For example, many such biasing mechanisms include undesirably expensive components and/or xe2x80x9ctoo manyxe2x80x9d components. Further, the size of the components and/or the complexity of the assembly can lead to warranty problems and/or unacceptably increase the cost of repair (i.e. xe2x80x9cin factoryxe2x80x9d repairs as well as xe2x80x9cin servicexe2x80x9d repairs in the field).
Another desired improvement is in the area of assembly. Many assemblies require multiple and complex fixtures for holding components together during assembly. The fixturing is often made considerably more complex where the biasing mechanism must be given a pre-tension and then held together until the assembly is sufficient to hold the biasing mechanism in its pre-tensioned state. It is noted that pre-tension is required, for example, to provide an initial level of support to a seated user""s upper torso before recline begins. The pre-tension forces can be considerable, particularly where the chair is adjustable for large or heavy persons, and where the torque arm on the biasing spring is small compared to the torque of the back upright that a seated user leans against. This results in a fixture that must be capable of applying considerable forces, yet that must do so safely and quickly.
In office chairs and public seating, the above problems are sometimes exacerbated by the appearance requirements of these products, because the products must provide optimal aesthetics in order to result in a sale. In modern times, many product designs have tended to include sleek and thin profiles, and hidden or minimally-sized functional components. This complicates and makes more difficult the design of long-lasting durable biasing mechanisms that are replaceable and repairable.
Accordingly, an apparatus is desired solving the aforementioned problems and having the aforementioned advantages.
In one aspect of the present invention, a jointed apparatus includes first and second structural members, a torsion spring adapted to pivotally support and rotationally bias the first structural member relative to the second structural member about a joint, an anchor for holding the first and second structural members together, and a pre-tensioning device that torsionally tensions the torsion spring as the first and second structural members, the torsion spring, and the anchor member are assembled together.
In another aspect of the present invention, a seating unit includes first and second elongated structural members pivoted together and defining a joint. A bushing is provided that includes a first section attached to the first structural member, a second section, and a torsion spring connecting the first and second sections. A pre-tensioning device engages the second section and the second structural member. The pre-tensioning device has angled surfaces that inter-engage to rotate the second section during assembly to pre-tension the torsion spring during assembly.
In another aspect of the present invention, a method comprises steps of attaching first and second structural members and a torsion spring together with an anchor to form a joint. The step includes torsionally pre-tensioning the torsion spring simultaneously and increasingly as the anchor is tightened in a direction parallel an axis of rotation defined by the joint and the joint is assembled together.
These and other aspects, objects, and features of the present invention will be understood and appreciated by those skilled in the art upon studying the following specification, claims, and appended drawings.